The present disclosure relates to implantable treatment devices, and more particularly to stents and other prostheses intended for fixation in body lumens especially including the esophagus
Stents are generally employed to open or keep open a body lumen. For example, carcinomas in the esophagus lead to progressive dysphagia, i.e. difficulty in swallowing, and the inability to swallow liquids in the most severe cases. While surgical removal is sometimes effective, the majority of patients have tumors that cannot be surgically removed. Repeated dilations of the body lumen of the esophagus provide only temporary relief.
Difficult or refractory cases often are treated by intubation using open wire weave prostheses or stents. An example of an open wire weave stent is provided in U.S. Pat. No. 4,800,882 (Gianturco), wherein is described such a device employed as an endovascular stent. These prostheses are frequently subject to migration. Self-expanding mesh stents also have been considered for use as esophageal prostheses. U.S. Pat. No. 4,655,771 (Wallsten) discloses a mesh stent as a flexible tubular braided structure formed of helically wound thread elements. Mesh stents appear unlikely to lead to pressure necrosis of the esophageal wall. The inherent scalability of mesh stents, as compared to a rigid plastic stents, makes them more easily inserted and the subsequent implantation causes much less trauma to the patient.
A difficulty with self-expanding stents concerns their accurate placement and deployment. Typically a tube surrounds the self-expanding stent and radially compresses the stent into a reduced-radius delivery configuration. With the stent positioned at a treatment site, the outer tube is axially withdrawn, permitting the stent to radially self-expand. However, the larger size of an esophageal stent (as compared to biliary and vascular applications, for example) gives rise to substantial friction at the stent/outer tubing interface. As a result, it is difficult to precisely maintain the position of the stent during deployment, and practically impossible to retract the stent after partial deployment.
Migration resistant stent designs include the addition of a mechanically lumen-bonding surface to the outer surface of a stent. U.S. Pat. No. 8,435,283 (Jordan et al) describes the addition of a cross hatch pattern of pyramids to the outer surface of a stent. The texture is intended to mechanically grasp tissue, and thereby anchor the stent. Such stents suffer from the disadvantage that dislocation by peristaltic motion causes inflammation of the inner lining of the body lumen, leading to infection, necrosis and possibly perforation.
Stenting of the esophagus has proven to be a particularly challenging stent application. The esophagus is a muscular lumen that is about ten inches long and extends from the hypopharynx to the stomach. The esophageal lumen is subject to wavelike contractions known as peristalsis, which pushes food down through the esophagus to the stomach.
Conventional stents utilized for the esophagus have significant drawbacks. Because the esophagus is very soft and flexible compared to other lumina, preventing migration of the stent is problematic. In particular, the esophagus frequently changes size and position, which causes complications for typical stents. For instance, a stent having a constant diameter along its entire axial length will have a tendency to migrate as the esophagus expands. The stricture is narrower than the lumen located proximally and distally of the stricture, and the stent is longer than the length of the stricture such that the portions of the stent proximately and distally of the stricture do not help prevent the stent from migrating. Therefore, there is an increased possibility that the stent will migrate within the lumen.
Moreover, the esophageal lumen is muscular and its wavelike contractions generally travel from its proximal end to its distal end resulting from an impulse applied at one side of the lumen wall. Due to the actions of the lumen, flexible stents have been designed to mimic the movement of the lumen. However, flexible stents may be prone to infolding or kinking, effectively occluding one or both of the openings of the stent. Furthermore, providing more rigid stents increases the risk of damage to the lumen of the esophagus, such as by damaging the blood vessels lining the lumen. Rigid stents are also typically more prone to migration.
A further difficulty with self-expanding esophageal stents is that they can cause gastrointestinal reflux. To place the self-expandable esophageal stent at a lesioned part of the stenosed gullet, an operator primarily shrinks the stent so as to reduce the cross section of the stent, installs the shrunken stent in a stent insertion device, and inserts the stent into the stenosed part of the gullet using the insertion device. After the stent reaches the stenosed part of the gullet, the stent is pushed so that the stent, usually fabricated from shape-memory alloy wires, is separated from the insertion device and elastically expands and restores its original shape, thus pushing the wall of the stenosed part outwards in radial directions and thereby enlarging the size of the passage of the stenosed part, making swallowing easier.
However, when the esophagus is stenosed near the stomach, where the esophageal sphincter is located, the esophageal stent must be placed in the lower end of the esophagus. Low end esophageal placement can open the esophageal sphincter causing gastrointestinal reflux. The presence of stomach acid in the esophagus can significantly complicate an already pathologic condition.
Accordingly, there is a need in the industry for a stent that is capable of conforming to a lumen and maintaining the opening through a stricture. In addition, there is a need for a stent that reduces migration and the possibility of obstruction of the stent openings.